Academic Argument Against the Stoics

"It was these statements of the Stoics that Arcesilaus controverted by proving that cognition is not a criterion intermediate between knowledge and opinion" (Sextus Empiricus, Against the Logicians I.153).

"If, then, impressions are cognitive in so far as they attract us to assent and to the following of them up with corresponding action, then, since false ones also are seen to be of this kind, we must declare that the non-cognitive impressions are indistinguishable from the cognitive" (Sextus Empiricus, Against the Logicians I.405).

"They summon the Stoics to face apparent facts. For in the case of things similar in shape but differing in substance it is impossible to distinguish the cognitive impression from the false and non-cognitive. If, for example, of two eggs that are exactly alike I offer each one in turn to the Stoic for him to distinguish between them, will the Sage be able on inspection to declare indubitably whether the egg exhibited is this one or that other one? And the same argument also holds good in the case of twins" (Sextus Empiricus, Against the Logicians I.408).
Plato died in 348/347 BCE. The Academy itself continued under new leadership.

When Arcesilaus became its head in 268/267 BCE, he refocused attention within Academy on the Socratic practice of asking questions to expose the pretense to wisdom.

"Arcesilaus... was the first to suspend his judgement owing to the contradictions of opposing arguments. He was also the first to argue on both sides of a question, and the first to meddle with the system handed down by Plato" (Diogenes Laertius, Lives of the Philosophers IV.6.28).

Cicero refers to the Academy with this changed focus as "the New Academy" (Academica I.46).

Academica II.40

They bring their whole case together in a single proof as follows: some impressions are true, others false; and, a false impression cannot be perceived; but, every true impression is such that one could also have a false impression just like it. And, when two impressions are such that they don’t differ at all, it isn’t possible that one of them can be perceived, while the other isn’t. Therefore, no impression is capable of being perceived. (40)

Lucullus does not present Academic argument very clearly, but we can see the idea.

The Academics use Socrates' questioning in dialectic against the Stoics.

The Stoics think that knowledge is possible. They think that we can get and assent to cognitive impressions and withhold our assent from noncogntive impressions. The Academics try to make the Stoics contradict themselves.

1.  For every true impression, there could be a false impression "just like it."
2.  If (1) is true, then it is always necessary to withhold assent.
3.  If it is always necessary to withhold assent, then knowledge is not possible.
4.  Knowledge is not possible.

This argument is valid. The Stoics accept (2) and (3). This leaves (1).

Academica II.54

They harp on the similarities of twins or of seals stamped from signet rings. Who on our side denies that similarities exist, given that they are apparent in many things? Yet if it is enough to do away with knowledge that many things are similar to many others, why aren’t you satisfied with that, especially when we concede it? Why do you go on to maintain something the nature of things does not permit, by denying that each thing is in its own kind and just as it is, i.e., that there aren’t any shared features that don’t differ at all between two or more things? Take it as granted that eggs are very similar to eggs, and bees to bees: what are you fighting for? What are you driving at with your twins? That they are similar—the point with which you could have been satisfied—is conceded; but your idea is that they aren’t similar but absolutely identical, which simply cannot happen. (54)

Lucullus denies that something is possible. To understand what, we need to distinguish two theses.

The first is that if x = y, then x and y are indiscernible. This is generally thought to be an uncontroversial truth about identity. The second thesis is that if x and y are indiscernible, then x = y.

Lucullus takes the Academics to think that it is possible for x and y to indiscernible but be distinct. The Stoics deny this is possible. They accept the second thesis. They think that indiscernibles are identical.

How does this bear on whether (1) is true in the Academic argument against the Stoics?

If "just like it" means indiscernible, then (1) is false.

In the proof, the background assumption is that some impressions are true. Let I be one such impression. Now, given the two theses about identity, we can derive a contradiction from the assumption that (1) is true.

If (1) is true, then given the background assumption, it follows that there could be a false impression indiscernible from I. Let I* be such a false impression. I is true, and I* is false. So it follows from the uncontroversial truth about identity that II*. If, however, indiscernibles are identical, it also follows that I = I*.

There is still the question of whether it is always humanly possible to tell the difference between the impressions.

You deny that there is such similarity between things in nature. ... You may well be right; but there could be one between our impressions. If so, that similarity deceives the senses—and if one similarity [involving twins] deceives them, it will render everything doubtful. For without the criterion by which he’s supposed to be recognized, even if the person you’re looking at actually is the person you think you’re looking at, you still won’t be judging by the mark you say we’re supposed to use to avoid false, but exactly alike, impressions (Academica II.84). Suppose that there are twins A and B and that someone who is looking at A gets the impression that he sees A. The Academics invite the Stoics to think that no matter how good the light is, how wide awake the person is, and so on, the person cannot rule out that his impression is one he gets from looking at B.

Academica II.57

I concede that the wise man himself—the subject of our whole discussion—will suspend his assent when confronted by similar things that he does not have marked off; and that he will never assent to any impression except one such that it could not be false. But he has a particular skill by which he can distinguish true from false impressions in normal cases and he must bring experience to bear on those similarities. Just as a mother discriminates her twins as her eyes become accustomed to them, so you, too, will discriminate them, if you practice. (57)

“Nor does this work against us, since it is all right for us not to be able to discriminate those eggs: that doesn’t make it any more reasonable to assent that this egg is that one, as if there were absolutely no difference between them. I have my rule—to judge such impressions true as cannot be false—from which I may not depart by a hair’s breadth (as they say), lest I confound everything. (58)

Lucullus makes two points.

He says that practice makes us better at distinguishing similar things.

He says that we do not need "to be able to discriminate those eggs." All we have to do is not assent in those cases.

How does this second point bear on the Academic argument against the Stoics?

Lucullus, it seems, is admitting that there could be false impressions "just like" some true impressions but denying that this poses a problem for the Stoics because it does not follow that no impression is cognitive.

Academica II.61

If we followed the Academics, we would be constrained by bonds that would prevent us from moving at all. For by doing away with assent, they have done away with every mental motion and practical action—something that not only can’t be done rightly, but can’t be done at all. (61)

This argument the Stoics press against the Academics is what is sometimes called the inactivity argument.

1.  Knowledge is not possible.
2.  If (1) is true, then assent is not permitted.
3.  If assent is not permitted, rational action is not possible.
4.  Rational action is not possible.

This reply to the Academics takes them to believe that (1) is true. This belief, though, if they have it, does not follow from the rules of dialectic. In the dialectic, the Academics play the role of questioner.

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